In mechanical timepieces, a paramount one of the component that governs the movement is the hairspring, which it is assembled with the balance staff and the stud to form part of the oscillating system.
For high accuracy time estimation, recent technology utilized the technique of micro-fabrication to manufacture high quality hairsprings.
However, the fragility of such micro-fabricated hairsprings, which are often formed from brittle materials like silicon or quartz and having a relative low strength, increases the likelihood of failure by way of fracture.
During assembly, when a hairspring is press-fitted onto a balance staff, extreme high contact pressure induced in the contact region breaks the collet or renders the collet in a state of stress which may result in fatigue failure.
In order to minimize stress from press-fitting of the hairspring collet, a flexible structure may be incorporated. When a collet is fitted onto the balance staff, the flexible structure may provide a degree of elastic deformation in order to release or reduce a portion of the stress induced.
However, the parameters of such hairspring design in a timepiece when using micro-fabrication techniques utilising such brittle materials, dictate difficulties in providing a suitable timepiece from functional and structural standpoints:                i. if a collet is sufficiently tight so as to suitably engage with the staff, the resultant stress in the collet may induce fracture during assembly or usage, and        ii. alternatively, if the collet allows for sufficient deformation to relieve the stress during assembly and usage, there may be insufficient frictional force to adequately secure the hairspring so as to resist rotational torque in use, the hairspring may not provide the functional requirements for a timepiece movement.        
In respect of fracture issues associated with a hairspring collet, within the literature some have sought to reduce the induced stress by designing the collet having specific geometries. For example, U.S. Pat. No. 7,758,237 discloses a collet designed having elastic arms, wherein the arm width is varied along different positions with a view to providing improved stress distribution.
Others, such as in U.S. Pat. No. 7,926,355 disclose a collet that has an alternating arrangement of a rigid area and an elastic area such to optimize the gripping force against the press-fit stress.
Other manners within the literature to fix a collet to a staff and reduce the likelihood of fracture include providing a loose fit collet, whereby the assembly process is performed by using some adhesives to glue the components individually